Add variation of ring-codec assoc-conj

[jconti]

Implements a variation on ring-codec's assoc-conj.

Resolves #86

[weavejester]

I'm in two minds about this one. It could be useful, but I worry it's too specific. You should also change the vector? check to coll? so it works with other collections, and get to find so it works with nil values.

[jconti]

I'm in two minds about this one. It could be useful, but I worry it's too specific. You should also change the vector? check to coll? so it works with other collections, and get to find so it works with nil values.

Thanks for the patience in getting back to this. I completely agree. Your suggestions did not occur to me, and seem obvious in retrospect. Thank you! Uncertain if this will improve it enough, but I will make these changes so it can be evaluated further.